Arrange the following in the order of property indicated for each set: `NH_(3) , PH_(3) , AsH_(3) , SbH_(3) , BiH_(3)` - increasing base strength.

Explanation

The order of increasing basic strength:
`BiH_(3)ltSbH_(3)ltAsH_(3)ltPH_(3)ltNH_(3)`
It is because, the presence of a lone pair of electrons on the central atom in `NH_(3) , PH_(3) , AsH_(3) , SbH_(3) and BiH_(3)`, makes them behave as Lewis bases. However, with increase in atomic size of the central atom from `NH_(3)` to `BiH_(3)` , the electron density decreases which leads to a decrease in the basic strength.